Wireless communication has become a popular way to communicate and is overtaking wired communication. Wireless communication is used for all kinds of communication including voice, data, etc. The popularity of wireless communication has resulted in setting up more wireless communication systems, including multiple-access systems, which are capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth and transmit power). Some examples of multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Multiple-access systems used in wireless communication can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations by sending transmissions on the forward and reverse links. The forward link, which is also referred to as the downlink, is the communication link from the base stations to the terminals or mobile stations. The reverse link, which is also referred to as the uplink, is the communication link from the terminals or mobile stations to the base stations. Both the forward link and reverse link can be established through a single-in-single-out system, multiple-in-single-out system, or a multiple-in-multiple-out (MIMO) system.
MIMO systems use multiple transmit antennas and multiple receive antennas for data transmission. Multicarrier systems, can provide improved performance by enabling the use of two or more carrier frequencies for information transmission, which can lead to higher throughput and/or greater reliability. However, there are problems associated with multicarrier systems which can affect their performance, such as the division of power among the multiple carriers. For example, the division and allocation of power among different multiple carriers can be difficult, and if it is not done correctly, can result in signal degradation.
Although some communication systems have increased the bandwidth available for wireless communication, there is still further demand brought on by the increased popularity of wireless communication. Techniques such as using multiple carrier frequencies to transmit more data have helped increase the available bandwidth but have introduced other problems. For example, both CDMA2000 and WCDMA are quickly becoming code-space limited in the forward link. This is occurring because the growth in capacity of these systems is limited by the available number of orthogonal codes. CDMA2000 has attempted to solve these capacity problems by introducing Quasi-Orthogonal Functions (QOF), which have the negative side effect of causing intra-sector interference. WCDMA has also attempted to solve this capacity problem by assigning extra PN codes to the same cell, which also has the negative side effect of causing intra-sector interference. In order to address the intra-sector interference produced by both of these approaches, cancellation techniques are used to increase downlink capacity. However, cancellation techniques can create other problems such as cancellation of desired signals.